Porter858

I'm helping a friend do a very low budget R-134a conversion on a 70 Cutlass supreme, and I'm not very familiar with the older style a/c systems.

He is re-using the original lines, only changed the dryer and expansion valve, four seasons rebuilt R-134a/A-6 compressor, o-rings, and oil. Stock POA valve, not re-calibrated.

My questions are:

Should the compressor ever cycle on and off?

Once you turn on the A/C part on the controller (both sets of points work) the clutch engages and stays on the whole time. When you move the controller back to the off position, the clutch still stays engaged. If you turn the engine off and restart it, then the compressor stops running until the a/c is turned on again.

Both the controller and the relay appear to be working correctly, is this how the original system was designed to work?

Texas69

That is the correct function for a 1969 model ( once ac is activated, the compressor will stay active until you turn off the car). Someone posted a mod on CO to allow the compressor to switch off using the dash controls. Not sure if the fuction is the same for 1970.

1970cs

The compressor will cycle depending on load and settings, it will also cycle when charge is low.

Yes, per your description of the operation of the clutch and controls is correct! I have a 70 Supreme with air and it seems strange but the service manual describes the operation as such.

Pat

Porter858

Thanks guys!

I just ran across a short post on ROP, and a guy mentioned taking apart the relay and cutting the jumper wire, but he wasn't specific on what exactly that would do. I wonder if that's the mod? I'll have to try to find that mod on here.

Lady72nRob71

If the POA is not recalibrated, the performance will be quite poor.
In keeping it low budget, just disconnect the large hose from the POA valve, reach in with a 7/32 socket on a stubby handle, and turn the cal screw 1/2 turn CCW as facing the screw.
This will get you close enough. A real cal and test can be done taking it off the car, using a set of AC gauges, an air compressor, and some hose and fittings...

And with a POA system,t he compressor runs continuously unlike cycling clutch systems.

Porter858

Thanks chiming in Rob! I tried to talk him into calibrating the poa valve after I ran across some of your posts about it last night, but he didn't want back track since it's a daily driver. It blows down to 41 on a 75 degree day, so I guess he's happy with it as is.

I'll try pitching this idea to him since you can leave it on the car. Thanks again for posting it, I'll be saving this info for my own cars.

MDchanic

To reiterate what Rob said, no, it won't.

The POA valve does the same job as a cycling pressure switch would in a newer system - it regulates the pressure in the system to keep the evaporator from getting too cold and freezing up. The compressor runs continuously, but the load on it varies.

And a 41° outlet temperature at 75° ambient is not impressive.
Let's see what his system does at 95°. If that temperature drop holds true, it will blow at 61°.

- Eric

Texas69

Here is a link to the mod I was referring to: https://classicoldsmobile.com/forums...-function.html

Excellent write-up by 69442C

Porter858

Thanks to everyone who replied!

Eric- I couldn't agree more, I tried to tell him the same thing, but it's not my car so I just let it go.

Texas - Thanks for posting that link, it's very informative!